The Wii wouldn't have had it's standout feature and thus lagged behind. However, if it still has it's Virtual console, then it certainly would have caught on with nostalgic (or should I say classic?) gamers.
It reminds me a bit of the scenarios in an old french gaming magazine as to how the Wii would play out. They had 3 options:
1. Just like the Gamecube, the Wii would tank and Nintendo go third party like Sega did before
2. Wii does okay, not really well but not super hot either (so probably like the XBO did this gen)
3. Everyone flocks to the Wii just because of the Virtual Console, reigning over the end of console gaming with it's classic games.
So yeah, my opinion is that the classic games of the virtual console would have pushed Nintendo sales somewhat. With that alone, I'm sure it would have beaten the Gamecube in total sales.
The other question is about how Twilight Princess would have been handled. Would the Gamecube version or the Wii version be scrapped since the technical difference between the two would be too great otherwise? If they scrapped the Cube version for the Wii HD, then that also would have given the console a nice starting boost.
Alas, I don't think it would have been enough to retain the gamers, who really were getting into real is brown territory so much that colors were eww for the usual hardgore dudebros who make up the biggest part of western console gamers.
So I think it would potentially have sold around what the XBO is doing, better than it's predecessors, but not really going anywhere big.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454
The Steam/GOG key gifting thread: https://gamrconnect.vgchartz.com/thread/242024/the-steamgog-key-gifting-thread/1/